The present disclosure relates to a miniaturized nuclear magnetic resonance (NMR) sample analyzer, as for analyzing drill cutting samples, which can be operated in a laboratory or wellsite.
NMR instruments have been widely used; for example, in the energy industry, for characterizing formation rock and fluid properties in-situ, as a well logging technology, and ex-situ as a core-plug measurement technology. Low-field laboratory NMR core analyzers have sometimes been used for analysis of drill cuttings, with limited success.
Although NMR is recognized as a valuable formation evaluation technology, its widespread use has been hindered by economic concerns and technical challenges. NMR logging has only been used in a small fraction of wells because of tool operation costs and costs associated with rig time, as the signal-to-noise ratio (SNR) at reservoir temperatures and for logging measurements are considerably poorer than laboratory measurements. Limited sample availability, long turn-around time, and measurement costs prohibit many uses of NMR core plug measurements, particularly for low-margin, low-porosity, tight reservoirs such as black shale plays.
Moreover, although drill cuttings are abundant and readily available, the accuracy of information extracted from cuttings using conventional low-field NMR analyzers is not always adequate. Current NMR logging and core analyzers are all classified as low-field NMR instruments which, from a signal-to-noise ratio (SNR) consideration, is a poor choice. However, because of confined borehole spaces and the availability of power delivery downhole, only low-field logging instruments can operate in these conditions.
For laboratory core analysis, conventional NMR core analyzers are built to accommodate typical core plug sizes, ranging from 1″ to 4″ in diameter and 1″ to 3″ in length, and use permanent magnets to control manufacturing and operation costs. Although these size ranges are desirable for analysis of conventional reservoir rocks such as sandstone and limestone, their large size makes it difficult to reduce magnet size, magnetic field strength, required RF power, RF amplifier wattage, and consequently the size and cost of the entire system.